Determination of the quantity, size, characteristics, and types of particulate matter in fluids is important for many applications such as monitoring fluids in engines and rotating machinery, industrial quality control, food processing, medical analysis, and environmental control. For example, as an engine ages, it flakes metal particulates into its lubricating oil. It is known that the size, number, and shape of particulates correspond to engine condition, and can alert one to imminent engine failure. Predicting failure is critically important in aircraft engines, where sudden failure could result in a crash and loss of life. Heretofore, oil particulates were checked by extracting an oil sample while the aircraft is on the ground, and sending the oil to a laboratory for testing. Although necessary for safety, this process is time consuming.
In the early stages of wear engines shed smaller particulates, on the order of 50 microns or less, and that these particulates have characteristic shapes indicative of the type, source, and nature of the wear. As the wear process progresses, the amount and size of particles increase. Sensing and identifying smaller particles allows early identification of faults, more time for corrective maintenance action, and fewer unexpected catastrophic failures. Current methods to accomplish this are costly, time consuming, use only a small sample of oil, and are not thorough in fault identification. Any system which can monitor particulates automatically in situ would increase engine life and availability. Similarly, blood cells are of the order of 20 microns or less, and such a system could also perform similarly automated blood counts.
Copending U.S. patent application 08/143,370 (attorney docket no. 74,852) by Reintjes et al. discloses a system which optically images a fluid flow, detects the image, and classifies the size and shape of particulates in the fluid. However, that system images an entire fluid line, such as an oil line in an engine. To do this effectively, without missing many particulates, the imaging system must have a large depth of view, which severely restricts the magnification by the optics between the pipe and the detector. With such a small magnification, that system cannot resolve extremely small particulates, for example 50 microns or smaller.